Just as time marches on, so do SASS releases. SASS (Standard Analysis
Software System) is the MPE supplied software that converts level 0 spacecraft
data to the data products that the PI receives. Since the last newsletter,
there have been ~20 SASS releases and corresponding installations at GSFC. The
group here has gotten very good at installing new SASS releases and has enough
processing capacity to eliminate any backlog. Currently we are caught up with
AO5 data sent from MPE, and PIs should receive their data within ~5-6 weeks of
the observation date. It takes approximately 4 weeks to get data from the
spacecraft to the USRSDC on an 8mm tape. The other two weeks are processing
and shipping time. To check data status, information on processing will soon
be available on the US ROSAT Science Data Center (USRSDC) home page via the
WWW. Users will also be able to reach this page from the HEASARC and the ROSAT
GOF pages.

Some PIs have been receiving reprocessed AO data. The original reason for the
reprocessing was to fix bugs in the older versions of SASS and add improved
data products. Some of the fixes include correction of the photon timing
problem, better background determination, better source detection, better
attitude determination through the use of the WFC startracker in the attitude
solution, and better data products such as SIMBAD source correlations for the
HRI. The other fundamental reason for the reprocessing is to provide a common
data format for the public archive. The Rationalized Data Format (RDF) was
developed jointly by the USRSDC and MPE (see ROSAT Newsletter Number 10, pg. 14
for more information) and is a true FITS format. The first RDF release was RDF
0.6 on May 1993 and after many iterations RDF 2.4 was used for the beginning
of the reprocessing in May 1994. The ROSAT Results Archive (RRA) (see page 13
in this issue for more information) came into being shortly thereafter and
further requirements were imposed on the RDF such as including a light curve
and adding various FITS keywords that help researchers make better use of the
archival data. This resulted in further RDF releases. To date there have been
28 RDF releases and currently reprocessing is using RDF 3.4. This RDF has been
agreed upon by both the USRSDC and MPE to be the final archival version.

Different SASS and RDF versions exist, and now to further confuse everyone
there are different processing and reprocessing versions or revisions. REV0
processing refers to ROSAT DAY (RODAY) 28 through RODAY 852 excluding the
survey. REV1 starts with RODAY 853 and goes through 1318 (observation dates
Sept. 18, 1992 to Dec. 21, 1993). REV2 starts with RODAY 1319 and keeps on
going. As a PI, all these reprocessings will only affect REV0 data. If your
observation was prior to RODAY 853 you will get a new data set in the mail that
was processed using REV2 and these NEW REV2 data will have a 6 month
proprietary time period. In general, most observations will not be that
greatly affected. All later observations will be reprocessed for the purpose
of creating a uniform archive and these data will not be distributed to PIs
since the difference between REV1 and REV2 is primarily a matter of formats.

There are two parts to the reprocessing: running SASS as REV2 and reformatting
the data using RDF 3.4. The latest SASS (version 7_7) with RDF 3.4 will insure
that data will be consistent on both sides of the Atlantic and can be used by
the staff to populate the RRA. Currently we have reprocessed data to RODAY 710
(exclusive of days 373-443) using REV2 but we have to apply RDF 3.4 to bring
the data to spec. RODAYS 711 to 1318 have to be reprocessed with REV2 and RDF
3.4. RODAYS 1319 to 1780 only have to have RDF 3.4 applied to them
(reformatting) while the rest of the data is up to spec.

In summary, AO5 and later data are flowing smoothly while reprocessing is being
done to achieve a uniform archive and most importantly to extract data into a
format that can be easily accessed by users. In the future, if there are
problems (with the gain, for example), the user will probably be able to run
project-provided software that will correct this problem. This will be
possible because required data such as "raw coordinates" are now accessible in
RDF 3.4. This is designed to alleviate the need for future reprocessings.